Such an electric switch for a power tool is recently disclosed, for instance, in Japanese patent laid-open publication No. 62-22331 (Japanese patent application No. 60-160916) of prior application. This switch internally includes a power transistor for controlling the rotor circuit of the motor, a printed circuit board carrying the control circuit for controlling the torque output of the motor, and a switch mechanism connected to the control circuit.
The switch mechanism is provided with first through third moveable contact pieces which, to form a switch contact circuit, depend from a moveable piece which synchronizes with the actuating force of the actuation lever, and as the moveable piece undergoes a sliding motion, the moveable contact pieces are each interposed between the adjacent surfaces of a pair of contact pieces which oppose each other as fixed contact pieces, and a desired contact signal is obtained by the contact pieces at the time of this interposing movement.
In this case, the adjacent contact pieces are supported in the switch casing so that they can expand and elastically deform in the direction of the contact motion in order to obtain a certain contact pressure.
Therefore, considerable cares are required in positioning these contact pieces in optimal fashion after they are press fitted and crimped, by taking into account their elastic deformations, so that the contact pieces may not touch the inner wall surfaces of the switch casing and they may contact with the moveable contact pieces with uniform pressure when the contact pieces have fully expanded. This factor contributed to the loss of the assembly work efficiency and, hence, the loss of the production efficiency of the switch mechanism.
In such a switch, since manual actuation of the slider takes place by way of a lever which engages the slider at its one end and protrudes externally of the switch casing, typically from a lower part thereof, and since the lever moves relatively to the switch casing, a special sealing structure must be incorporated in the slot through which the actuation lever protrudes so as to accommodate the motion of the actuation lever with respect to the switch casing.
Further, the upper part of the switch casing must define an open cavity for the convenience of installing the switch contact mechanism therein and must be closed thereafter. Thus, as can be readily understood, the structure of the upper part of the switch casing is highly important in simplifying the assembly process thereof and ensuring the reliability of the switch contacts by protecting them from external influences.